Determining method, computer product, determining apparatus, and determining system

ABSTRACT

A determining method executed by a processor includes obtaining distance information that indicates a distance between monitoring apparatuses disposed to encompass a given area in which wireless communications apparatuses are scattered; causing a wireless signal to be transmitted and received between the monitoring apparatuses by multi-hop communication among the wireless communications apparatuses; calculating an estimated distance between the monitoring apparatuses, based on a hop count of the wireless signal multi-hop communicated among the monitoring apparatuses; and making a determination concerning a vacant area in which none of the wireless communications apparatuses is present, based on a result of comparison of the distance indicated by the obtained distance information and the calculated estimated distance.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of InternationalApplication PCT/JP2012/071230, filed on Aug. 22, 2012 and designatingthe U.S., the entire contents of which are incorporated herein byreference.

FIELD

The embodiments discussed herein are related to a determining method, adetermining program, a determining apparatus, and a determining system.

BACKGROUND

A technique of using multiple receiving apparatuses and multiplewireless terminals to determine the position of a wireless terminal isknown (for example, refer to Japanese Laid-Open Patent Publication No.2007-221541). Further, a radio frequency identification (RFID) systemthat uses multiple monitoring apparatuses and multiple nodes (wirelesssensor, etc.) is known (for example, refer to Japanese Laid-Open PatentPublication No. 2010-213278).

According to another known technique, in an ad hoc network, thedistances between a mobile terminal apparatus and multiple base stationsare estimated based on the hop counts from the mobile terminal apparatusto the base stations, and based on a result of the estimation, theposition of mobile terminal apparatus is estimated (for example, referto Japanese Laid-Open Patent Publication No. 2006-229845). Further, aknown sensor network (wireless sensor network) is a wireless network inwhich multiple wireless terminals equipped with sensors are scatteredand the wireless terminals cooperate to obtain an environment or aphysical state.

SUMMARY

According to an aspect of an embodiment, a determining method executedby a processor includes obtaining distance information that indicates adistance between monitoring apparatuses disposed to encompass a givenarea in which wireless communications apparatuses are scattered; causinga wireless signal to be transmitted and received between the monitoringapparatuses by multi-hop communication among the wireless communicationsapparatuses; calculating an estimated distance between the monitoringapparatuses, based on a hop count of the wireless signal multi-hopcommunicated among the monitoring apparatuses; and making adetermination concerning a vacant area in which none of the wirelesscommunications apparatuses is present, based on a result of comparisonof the distance indicated by the obtained distance information and thecalculated estimated distance.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram (part 1) depicting an example of determination by adetermining system according to a first embodiment;

FIG. 2 is a diagram (part 2) depicting an example of determination bythe determining system according to the first embodiment;

FIG. 3 is a diagram depicting an example of a hardware configuration ofa determining apparatus and monitoring apparatuses;

FIG. 4 is a diagram depicting an example of a hardware configuration ofa node;

FIG. 5 is a diagram depicting an example of a configuration of thedetermining apparatus according to the first embodiment;

FIG. 6 is a flowchart depicting one example of operation of thedetermining apparatus according to the first embodiment;

FIG. 7 is a sequence diagram of an example of hop count monitoringoperation by the determining system;

FIG. 8 is a diagram depicting a calculation example of an estimateddistance based on hop count;

FIG. 9 is a diagram depicting an example of the determining systemaccording to a second embodiment;

FIG. 10 is a diagram (part 1) depicting an example of estimation curvecorrection by the determining system;

FIG. 11 is a diagram (part 2) depicting an example of estimation curvecorrection by the determining system;

FIG. 12 is a diagram (part 3) depicting an example of estimation curvecorrection by the determining system;

FIG. 13 is a diagram depicting an example of a configuration of thedetermining apparatus according to the second embodiment;

FIG. 14 is a flowchart depicting an example of determination operationof the determining apparatus according to the second embodiment; and

FIG. 15 is a flowchart depicting an example of correction operation ofthe determining apparatus according to the second embodiment.

DESCRIPTION OF EMBODIMENTS

Embodiments of a determining method, a determining program, adetermining apparatus, and a determining system will be described indetail with reference to the accompanying drawings.

FIG. 1 is a diagram (part 1) depicting an example of determination by adetermining system according to the first embodiment. As depicted inFIG. 1, a determining system 100 according to the first embodimentincludes a determining apparatus 110 and monitoring apparatuses 121 to128.

The determining apparatus 110 is an apparatus that can communicate withthe monitoring apparatuses 121 to 128. Further, the determiningapparatus 110 may be an apparatus that is provided separately from themonitoring apparatuses 121 to 128, or may be an apparatus that isprovided in any one of the monitoring apparatuses 121 to 128. In theexample depicted in FIG. 1, the determining apparatus 110 is provided inthe monitoring apparatus 121.

The monitoring apparatuses 121 to 128 are arranged to encompass a givenarea 101. The monitoring apparatuses 121 to 128 monitor a signaltransferred by multi-hop communication in a node group 102. Multi-hopcommunication, for example, is communication without an intermediateaccess point, by multi-step communication among numerous terminals (thenode group 102). In the given area 101, the nodes of the node group 102are scattered. The given area 101, for example, is an area filled withmatter such as concrete, soil, water, air, etc. Alternatively, the givenarea 101 may be an area in a vacuum state such as cosmic space.

The node group 102 are wireless communications apparatuses forming asensor network. More specifically, each node of the node group 102 is awireless communications apparatus capable of communicating wirelesslywith a nearby wireless communications apparatus. Further, each of thenodes of the node group 102 has sensors that detect temperature,pressure, sound, etc. and transmit wireless signals indicating sensingresults obtained by the sensor.

Each of the nodes of the node group 102 receives wireless signalstransmitted from nearby nodes and by forwarding the received wirelesssignals to nearby nodes, transfer the wireless signals by multi-hop. Asa result, a wireless signal transmitted by a node of the node group 102is transferred by other nodes of the node group 102 via multi-hop, andis transmitted by nearby wireless communications apparatuses (e.g., themonitoring apparatuses 121 to 128) in the given area 101.

The wireless signals transmitted by the nodes of the node group 102include hop count information that indicates the hop count from theinitial transmission source. The hop count is a number that indicatesthe number of times a signal is transmitted in multi-hop communication,from the initial transmission source and, for example, is a number thatresults when 1 is added to the transfer count from the initialtransmission source. When transferring a wireless signal, each of thenodes of the node group 102 increment the hop count included in thewireless signal that is to be transferred. As a result, when receiving awireless signal, a nearby wireless communications apparatus in the givenarea 101 can obtain information indicating the number of hops for thereceived wireless signal to reach the nearby wireless communicationsapparatus by multi-hop.

The nodes of the node group 102, for example, are arranged in the givenarea 101 by being strewn about in the given area 101 or by being mixedin matter filling the given area 101. Therefore, the position of eachnode of the node group 102 is unknown. Further, there is unevenness inthe arrangement of the nodes of the node group 102; and in the givenarea 101, a vacant area 103 may exist in which no node is present. Inaddition, a vacant area 103 in which no node is present may occurconsequent to an object such as a pillar in the given area 101. Forexample, the vacant area 103 is an area of a size in which nodes locatedon opposite sides cannot directly transmit or receive wireless signalswith respect to each other since the radio waves do not reach that far.

The determining apparatus 110 uses the monitoring apparatuses 121 to128, makes a determination concerning vacant areas 103 in the given area101, and outputs determination result. The determination concerning avacant area 103, for example, is a determination of whether a vacantarea 103 is present. As a result, when a determination result is outputfrom the determining apparatus 110 and indicates that a vacant area 103is present in the given area 101, the user can remix the matter fillingthe given area 101 and remove the vacant area 103.

The determination concerning the vacant area 103 may be a determinationof the position of the vacant area 103, a determination of the range ofthe vacant area 103, and the like. As a result, based on thedetermination result output from the determining apparatus 110 andconcerning the position and/or range of the vacant area 103, the usercan add nodes to the vacant area 103 and remove the vacant area 103.

Removal of the vacant area 103 makes the arrangement of the nodes of thenode group 102 in the given area 101 more uniform and enables moreefficient multi-hop communication of wireless signals. Removal of thevacant area 103 enables improvement of the accuracy of the determinationof node position based on the hop count described hereinafter. If therange of the vacant area 103 is to be determined by the determiningapparatus 110, in the determination of node position based on the hopcount described hereinafter, correction of the estimated position of anode, based on the range of the vacant area 103 becomes possible. As aresult, the accuracy of the determination of node position can beimproved.

<Hop Count Monitoring Operation>

As depicted in FIG. 1, under the control of the determining apparatus110, the monitoring apparatus 121 transmits a survey signal to nodesthat are near the monitoring apparatus 121 and among the node group 102.The survey signal is a wireless signal that includes hop countinformation indicating the hop count from the monitoring apparatus thatis the initial transmission source.

Each node of the node group 102, upon receiving the survey signal,increments the hop count of the hop count information included in thereceived survey signal and transmits in a vicinity thereof, a surveysignal in which the hop count indicated by the hop count information hasbeen incremented. As a result, the survey signal transmitted by themonitoring apparatus 121 is multi-hop transferred while the hop count ofthe hop count information is incremented by the node group 102, and istransmitted by the monitoring apparatuses 122 to 128. The monitoringapparatuses 122 to 128 transmit the hop count information included inthe received survey signal to the determining apparatus 110.

For example, the hop count of the survey signal received by themonitoring apparatus 122 is assumed to be 4 and the hop count of thesurvey signal received by the monitoring apparatus 123 is assumed to be6. If the monitoring apparatuses 122 to 128 receive, via multiple paths,the survey signal transmitted from the monitoring apparatus 121, of thehop count information of the received survey signals, the monitoringapparatuses 122 to 128 transmit to the determining apparatus 110, thehop count information having the smallest hop count.

For example, the monitoring apparatuses 122 to 128 transmit to thedetermining apparatus 110, the hop count information of the surveysignal that is transmitted from the monitoring apparatus 121 and firstreceived. The survey signal having hop count information indicating thesmallest hop count is frequently the survey signal transferred bymulti-hop, through the shortest path among multiple paths and therefore,the hop count information indicating the smallest hop count can betransmitted to the determining apparatus 110.

The distances between the monitoring apparatus 121 and the monitoringapparatuses 122 to 128 are substantially proportional to the hop countsof the survey signal that the monitoring apparatuses 122 to 128 receivefrom the monitoring apparatus 121. However, a vacant area 103 is presentbetween the monitoring apparatus 121 and the monitoring apparatus 124and therefore, the survey signal transmitted from the monitoringapparatus 121 is detoured about the vacant area 103 and received by themonitoring apparatus 124. Consequently, the hop count of the surveysignal received by the monitoring apparatus 124 is 9 and is notproportional to the actual distance between the monitoring apparatus 121and the monitoring apparatus 124.

Under the control the determining apparatus 110, the monitoringapparatuses 122 to 128 also sequentially transmit the survey signal,similar to the monitoring apparatus 121. The monitoring apparatuses 121to 128 transmit to the determining apparatus 110, the hop countinformation included in a survey signal that is received by multi-hopcommunication of the node group 102 and transmitted by anothermonitoring apparatus. As a result, for each monitoring apparatuscombination of the monitoring apparatuses 121 to 128, the determiningapparatus 110 can obtain the hop counts between the monitoringapparatuses.

Further, for example, the monitoring apparatuses 121 to 128 transmit thesurvey signal by the same transmission power as the nodes of the nodegroup 102. As a result, drops in the accuracy of the calculation of theestimated distance based on hop count, occurring consequent to thereached distance of the survey signal transmitted by the monitoringapparatuses 121 to 128 and the reached distance of the survey signaltransmitted by the nodes of the node group 102 differing, can beprevented.

<Obtaining Actual Distance Between Monitoring Apparatuses>

The determining apparatus 110, for each monitoring apparatus combinationof the monitoring apparatuses 121 to 128, obtains distance informationthat indicates the actual distance between the monitoring apparatuses.The distance information, for example, is stored to the memory of thedetermining apparatus 110, in advance. The determining apparatus 110 mayobtain the distance information by calculation based on information thatindicates position coordinates of the monitoring apparatuses 121 to 128.Further, the position coordinates of the monitoring apparatuses 121 to128, for example, may be stored in the memory of the determiningapparatus 110, in advance, or may be obtained from the monitoringapparatuses 121 to 128.

<Calculation of Estimated Distance Based on Hop Count>

The determining apparatus 110, based on the obtained hop count and foreach monitoring apparatus combination of the monitoring apparatuses 121to 128, calculates an estimated distance between the monitoringapparatuses. Calculation of the estimated distance based on hop countwill be described hereinafter (for example, refer to FIG. 8).

<Extraction of Monitoring Apparatus Combination for which EstimatedDistance and Actual Distance Differ>

FIG. 2 is a diagram (part 2) depicting an example of determination bythe determining system according to the first embodiment. In FIG. 2,portions identical to those in FIG. 1 are given the same referencenumerals used in FIG. 1 and description thereof is omitted. Thedetermining apparatus 110 calculates for each monitoring apparatuscombination of the monitoring apparatuses 121 to 128, the difference ofthe calculated estimated distance and the obtained actual distance.

The determining apparatus 110 extracts from among the monitoringapparatus combinations of the monitoring apparatuses 121 to 128, acombination for which the calculated difference is a given threshold orgreater. As a result, from among the monitoring apparatus combinationsof the monitoring apparatuses 121 to 128, a combination of monitoringapparatuses between which a vacant area 103 is present can be extracted.In the example depicted in FIG. 2, the combination of the monitoringapparatuses 121 and 124, the combination of the monitoring apparatuses122 and 125, and the combination of the monitoring apparatuses 123 and126 are assumed to be extracted.

<Calculation of Straight Line Connecting Extracted MonitoringApparatuses>

The determining apparatus 110, as depicted in FIG. 2, calculates foreach extracted monitoring apparatus combination, a straight lineconnecting the monitoring apparatuses. More specifically, the positioncoordinates of each monitoring apparatus are respectively assumed to be(x1, y1) and (x2, y2). The position coordinates of the monitoringapparatuses, for example, are stored in the memory of the determiningapparatus 110, in advance. The determining apparatus 110 substitutes x1,y1, x2, and y2 into (y2−y1)x+(x2−x1)y+x2y1−x1y2=0 and thereby,calculates a straight line connecting the monitoring apparatuses. In theexample depicted in FIG. 2, straight lines 211 to 213 are calculated.

<Calculation of Intersection of Straight Lines>

The determining apparatus 110 calculates intersections of the calculatedstraight lines 211 to 213. More specifically, the determining apparatus110 calculates the solution to a system of equations of the straightlines 211 to 213 and thereby, calculates intersections of the straightlines 211 to 213. In the example depicted in FIG. 2, intersections 221to 223 are calculated.

<Calculation of Center of Gravity of Intersections>

The determining apparatus 110 calculates the center of gravity of thecalculated intersections 221 to 223. More specifically, assuming theposition coordinates of the intersections are (x1, y1), (x2, y2), . . ., (xm, ym), the determining apparatus 110 can calculate positioncoordinates of the center of gravity by ((x1+x2+ . . . +xm)/m, (y1+y2+ .. . +ym)/m). In the example depicted in FIG. 2, m=3 and a center ofgravity 230 is calculated.

<Vacant Area Determination>

The determining apparatus 110 determines that a range encompassed by acircle 240 that includes the calculated intersections 221 to 223 and hasa center at the calculated center of gravity 230 is a vacant area 103.For example, the determining apparatus 110 calculates the distancebetween the center of gravity 230 and the intersections 221 to 223. Morespecifically, the position coordinates of the center of gravity and theposition coordinates of an intersection are assumed to be (x1, y1) and(x2, y2), respectively. In this case, the determining apparatus 110 cancalculate the distance between the center of gravity and theintersection by √((x2−x1)²+(y2−y1)²).

The determining apparatus 110, with respect to (x−x1)²+(y−y1)²=r²,substitutes the position coordinates (x1, y1) of the center of gravity230 for x1, y1, and substitutes the greatest value of the distancesbetween the center of gravity 230 and the intersections 221 to 223 forr. As a result, the circle 240 that includes the calculatedintersections 221 to 223 and has a center at the calculated center ofgravity 230 can be calculated. The determining apparatus 110, forexample, outputs the circle 240 as a determination result.

FIG. 3 is a diagram depicting an example of a hardware configuration ofthe determining apparatus and the monitoring apparatuses. Thedetermining apparatus 110 and the monitoring apparatuses 121 to 128depicted in FIGS. 1 and 2, for example, can be realized by aninformation processing apparatus 300 depicted in FIG. 3. The determiningapparatus 110 and the monitoring apparatus 121 may be realized byrespectively separate information processing apparatuses 300 or may berealized by a single information processing apparatus 300.

The information processing apparatus 300, for example, runs on anexternal power source. Further, the information processing apparatus 300includes a CPU 301, memory 302, a communications unit 303, an antenna304, an input/output interface 305, and a bus 310. The CPU 301, thememory 302, the communications unit 303, and the input/output interface305 are connected by the bus 310.

The CPU 301 (central processing unit) governs overall control of theinformation processing apparatus 300. The memory 302 is, for example, astorage apparatus that includes main memory and auxiliary memory. Themain memory, for example, is random access memory (RAM). The main memoryis used as a work area of the CPU 301. The auxiliary memory, forexample, is nonvolatile memory such as a magnetic disk, an optical disk,and flash memory. The auxiliary memory stores various programs thatcause the information processing apparatus 300 to operate. The programsstored in the auxiliary memory are loaded to the main memory andexecuted by the CPU 301.

The communications unit 303 wirelessly communicates with othercommunications apparatuses, via the antenna 304. For example, thecommunications unit 303 wirelessly communicates with the determiningapparatus 110 and nearby nodes among the node group 102. Further,communication between the communications unit 303 and the determiningapparatus 110 may be by a physical line. The communications unit 303 iscontrolled by the CPU 301.

The input/output interface 305, for example, includes an input devicethat receives operational input from the user, and an output device thatoutputs information to the user, etc. The input device, for example, canbe realized by keys (e.g., a keyboard), a remote controller, and thelike. The output device, for example, can be realized by a display, aspeaker, and the like. Further, the input device and the output devicemay be realized by a touch panel and the like. The input/outputinterface 305 is controlled by the CPU 301.

The information processing apparatus 300 receives sensing informationfrom the communications unit 303 and aggregates the sensing informationtransmitted from the node group 102. The information processingapparatus 300 outputs the aggregated sensing information from theinput/output interface 305. The information processing apparatus 300 maytransmit the aggregated sensing information, from the communicationsunit 303, through a network such as the Internet, to an externalapparatus such as a user terminal and a server.

FIG. 4 is a diagram depicting an example of a hardware configuration ofa node. Each node of the node group 102, for example, can be realized bya wireless communications apparatus 400 depicted in FIG. 4. The wirelesscommunications apparatus 400 includes a harvester 401, a battery 402, apower control unit 403, a sensor 404, a MCU 405, a wirelesscommunications unit 406, an antenna 407, and a bus 410.

The harvester 401 generates power based on the external environment ofthe installation site of the wireless communications apparatus 400,e.g., energy changes such as changes in light, vibration, temperature,radio waves (received radio waves) and the like. The battery 402 storespower generated by the harvester 401. The power control unit 403provides the power stored in the battery 402 to components of thewireless communications apparatus 400.

The sensor 404, the MCU 405, and the wireless communications unit 406are connected by the bus 410. The sensor 404 detects a givendisplacement at the installation site of the wireless communicationsapparatus 400. For example, a piezoelectric element that detects voltageat the installation site, a photoelectric element that detects light,and the like can be used as the sensor 404.

The MCU 405 (micro control unit) processes data concerning detection bythe sensor 404 and transmits the processed data as a wireless signal tothe wireless communications unit 406. Further, the MCU 405 controls thewireless communications unit 406 to increment the hop count of the hopcount information included in a wireless signal received by the wirelesscommunications unit 406 and to transmit to communications apparatusesnear the wireless communications apparatus 400, a wireless signal havinghop count information in which the hop count has been incremented.

The wireless communications unit 406, via the antenna 407, wirelesslycommunicates with the communications apparatuses near the wirelesscommunications apparatus 400. The communications apparatuses near thewireless communications apparatus 400, for example, are the monitoringapparatuses 121 to 128, and other nodes of the node group 102.

FIG. 5 is a diagram depicting an example of a configuration of thedetermining apparatus according to the first embodiment. As depicted inFIG. 5, the determining apparatus 110 according to the first embodiment,for example, includes an obtaining unit 501, a control unit 502, acalculating unit 503, and a determining unit 504. The obtaining unit 501obtains, for each monitoring apparatus combination of the monitoringapparatuses 121 to 128, distance information indicating the actualdistance between the monitoring apparatuses. The obtaining unit 501notifies the determining unit 504 of the distance indicated by theobtained distance information.

The control unit 502 controls the monitoring apparatuses 121 to 128 byperforming communication with the monitoring apparatuses 121 to 128. Thecontrol unit 502 transmits and receives the survey signals between themonitoring apparatuses 121 to 128, by the multi-hop communication by thenode group 102. Further, the control unit 502 obtains from themonitoring apparatuses 121 to 128, the hop count information of thetransmitted and received survey signals. The control unit 502 notifiesthe calculating unit 503 of the hop count indicated by the obtained hopcount information.

The calculating unit 503 calculates based on the hop count notified bythe control unit 502 and for each monitoring apparatus combination ofthe monitoring apparatuses 121 to 128, an estimated distance between themonitoring apparatuses. The calculating unit 503 notifies thedetermining unit 504 of the calculated estimated distance.

Based on a comparison result of the distance notified by the obtainingunit 501 and the estimated distance notified by the calculating unit503, the determining unit 504 makes a determination about the vacantarea 103 in which no wireless communications apparatus of the node group102 in the given area 101 is present, and outputs a result of thedetermination.

The obtaining unit 501, for example, can be realized by the CPU 301 andthe memory 302 depicted in FIG. 3. The control unit 502, for example,can be realized by the CPU 301 and the communications unit 303 depictedin FIG. 3. The calculating unit 503 and the determining unit 504, forexample, can be realized by the CPU 301 depicted in FIG. 3. Further, thedetermination result output from the determining unit 504, for example,is output to an external destination by the communications unit 303and/or the input/output interface 305.

FIG. 6 is a flowchart depicting one example of operation of thedetermining apparatus according to the first embodiment. The determiningapparatus 110 according to the first embodiment, for example, executesthe following operations. The determining apparatus 110 determineswhether a survey has been performed by each monitoring apparatus (themonitoring apparatuses 121 to 128) (step S601). If surveys have not beenperformed by all of the monitoring apparatuses (step S601: NO), thedetermining apparatus 110 causes a survey signal to be transmitted froma monitoring apparatus that is among the monitoring apparatuses 121 to128 and has not performed a survey (step S602).

The determining apparatus 110, with respect to the survey signaltransmitted at step S602, obtains the hop counts to each monitoringapparatus (step S603), and returns to step S601. At step S603, morespecifically, the determining apparatus 110 obtains the hop countinformation included in the received survey signal, from a monitoringapparatus that is among the monitoring apparatuses 121 to 128 and isother than the monitoring apparatus caused to transmit the survey signalat step S602.

At step S601, if a survey has been performed by each monitoringapparatus (step S601: YES), the determining apparatus 110 calculates anestimated distance between the monitoring apparatuses, based on the hopcounts obtained at step S603 (step S604). The determining apparatus 110further obtains the actual distance between the monitoring apparatuses(step S605).

The determining apparatus 110 determines whether a monitoring apparatuscombination is present for which the difference of the estimateddistance calculated at step S604 and the actual distance obtained atstep S605 is a threshold or greater (step S606), The threshold, forexample, is stored in the memory of the determining apparatus 110, inadvance. If no combination is present for which the difference of theestimated distance and the actual distance is the threshold or greater(step S606: NO), the determining apparatus 110 determines that nonode-vacant area is present in the given area 101 (step S607), and endsa series of the operations.

At step S606, if a combination is present for which the difference ofthe estimated distance and the actual distance is the threshold orgreater (step S606: YES), the determining apparatus 110 determineswhether one combination is present for which the difference of theestimated distance and the actual distance is the threshold or greater(step S608). If one combination is present for which the difference ofthe estimated distance and the actual distance is the threshold orgreater (step S608: YES), the determining apparatus 110 determines thata node-vacant area is present between the monitoring apparatuscombination for which the difference of the estimated distance and theactual distance is the threshold or greater (step S609), and ends aseries of the operations.

At step S608, if the number of combinations for which the difference ofthe estimated distance and the actual distance is the threshold orgreater is not one (step S608: NO), the determining apparatus 110determines whether two combinations are present for which the differenceof the estimated distance and the actual distance is the threshold orgreater (step S610). If two combinations are present for which thedifference of the estimated distance and the actual distance is thethreshold or greater (step S610: YES), the determining apparatus 110calculates for each of the combinations, a straight line connecting themonitoring apparatuses of the combination (step S611).

The determining apparatus 110 calculates an intersection of the straightlines calculated at step S611 (step S612). The determining apparatus 110determines that a node-vacant area is present at the intersectioncalculated at step S612 (step S613), ends a series of the operations.

At step S610, if the number of combinations for which the difference ofthe estimated distance and the actual distance is the threshold orgreater is three or more (step S610: NO), the determining apparatus 110transitions to step S614. In other words, the determining apparatus 110calculates for each of the combinations for which the difference of theestimated distance and actual distance is the threshold or greater, astraight line connecting the monitoring apparatuses of the combination(step S614).

The determining apparatus 110 calculates intersections of the straightlines calculated at step S614 (step S615), and calculates the center ofgravity of the intersections calculated at step S615 (step S616). Thedetermining apparatus 110 determines a circle that includes theintersections calculated at step S615 and has a center at the center ofgravity calculated at step S616 to be a node-vacant area (step S617),and ends a series of the operations.

FIG. 7 is a sequence diagram of an example of hop count monitoringoperation by the determining system. For example, by providing thedetermining apparatus 110 in the monitoring apparatus 121, themonitoring apparatus 121 becomes a master, the monitoring apparatuses122 to 128 become slaves, and monitoring operations are performed.

The monitoring apparatus 121 transmits to the monitoring apparatuses 122to 128, a notification request signal requesting notification of the hopcount (step S701). The monitoring apparatus 121 wirelessly transmits asurvey signal to nodes that are of the node group 102 and near themonitoring apparatus 121 (step S702). As a result, the survey signaltransmitted by the monitoring apparatus 121 is multi-hop transferred bythe node group 102, and the multi-hop transferred survey signal isreceived by the monitoring apparatuses 122 to 128.

The monitoring apparatuses 122 to 128 notify the monitoring apparatus121 of the hop count of the received survey signal (step S703). As aresult, the monitoring apparatus 121 can obtain the respective hopcounts between the monitoring apparatus 121 and the monitoringapparatuses 122 to 128.

The monitoring apparatus 121 transmits to the monitoring apparatus 122,a survey request signal requesting performance of a survey (step S704).The monitoring apparatus 122 transmits to the monitoring apparatuses121, 123 to 128, a notification request signal requesting notificationof the hop count (step S705). The monitoring apparatus 122 wirelesslytransmits a survey signal to nodes that are of the node group 102 andnear the monitoring apparatus 122 (step S706). As a result, the surveysignal transmitted by the monitoring apparatus 122 is multi-hoptransferred by the node group 102, and the multi-hop transferred surveysignal is received by the monitoring apparatuses 121, 123 to 128.

The monitoring apparatuses 121, 123 to 128 notify the monitoringapparatus 122 of the hop count of the received survey signal (stepS707). The monitoring apparatus 122 notifies the monitoring apparatus121 of a result of aggregation of the hop counts notified at step S707(step S708). As a result, the monitoring apparatus 121 can obtain therespective hop counts between the monitoring apparatus 122 and themonitoring apparatuses 121, 123 to 128.

The monitoring apparatus 121, similar to the monitoring apparatus 122,transmits a survey request signal to the monitoring apparatuses 123 to127, thereby causing surveys to be performed, and obtains the respectivehop counts.

The monitoring apparatus 121 transmits to the monitoring apparatus 128,a survey request signal requesting performance of a survey (step S709).The monitoring apparatus 128 transmits to the monitoring apparatuses 121to 127, a notification request signal requesting notification of the hopcount (step S710). The monitoring apparatus 128 wirelessly transmits asurvey signal to nodes that are of the node group 102 and near themonitoring apparatus 128 (step S711). As a result, the survey signaltransmitted by the monitoring apparatus 128 is multi-hop transferred bythe node group 102, and the multi-hop transferred survey signal isreceived by the monitoring apparatuses 121 to 127.

The monitoring apparatuses 121 to 127 notify the monitoring apparatus128 of the hop count of the received survey signal (step S712). Themonitoring apparatus 128 notifies the monitoring apparatus 121 of aresult of aggregation of the hop counts notified at step S712 (stepS713). As a result, the monitoring apparatus 121 can obtain therespective hop counts between the monitoring apparatus 128 and themonitoring apparatuses 121 to 127.

Further, before the monitoring operations depicted in FIG. 7, each nodeof the node group 102 may be charged. Charging of the nodes of the nodegroup 102, for example, can be performed according to the type of theharvester 401 depicted in FIG. 4. For example, if the harvester 401generates power by environmental electromagnetic waves, the nodes of thenode group 102 can be charged by providing to the given area 101,electromagnetic waves for charging the nodes.

As a result, the nodes of the node group 102 can more assuredly and atthe same power, transmit the survey signal and therefore, the actualdistance between the monitoring apparatuses and the hop count of thesurvey signal become easier to proportionalize. Therefore, a moreaccurate estimated distance between the monitoring apparatuses can becalculated. Charging of the nodes of the node group 102, for example,can be performed by the determining apparatus 110.

FIG. 8 is a diagram depicting a calculation example of the estimateddistance based on hop count. As described, for each of the monitoringapparatus combinations of the monitoring apparatuses 121 to 128, thedetermining apparatus 110 calculates an estimated distance between themonitoring apparatuses, based on hop counts.

FIG. 8 depicts a partial area 801 that is in the given area 101 andbetween the monitoring apparatus 121 and the monitoring apparatus 126.Nodes 811 to 816 represent nodes that are among the node group 102 andincluded in the partial area 801. In FIG. 8, the nodes 811 to 816 areassumed to be arranged at even intervals in a straight line.

The determining apparatus 110 obtains an average distance 802 betweenthe nodes of the node group 102 in the given area 101. For example, thedetermining apparatus 110 calculates the distance 802 between the nodes,based on the density [nodes/area] of the node group 102 in the givenarea 101. More specifically, assuming the density of the node group 102in the given area 101 to be ρ, the distance 802 between the nodes can becalculated by 1/√ρ.

The determining apparatus 110 obtains a reachable distance 803 of radiowaves transmitted by the nodes of the node group 102. The reachabledistance 803 of the radio waves, for example, is stored to the memory ofthe determining apparatus 110, in advance.

The determining apparatus 110 can calculate an estimated distancebetween the monitoring apparatuses by (distance between nodes)×(hopcount), when (distance between nodes)≦(reachable distance of radiowave)<(distance between nodes)×2 is true. Further, the determiningapparatus 110 can calculate an estimated distance between the monitoringapparatuses by (distance between nodes)×2×(hop count), when (distancebetween nodes)×2≦(reachable distance of radio wave)<(distance betweennodes)×3 is true.

Similarly, the determining apparatus 110 can calculate an estimateddistance between the monitoring apparatuses by (distance betweennodes)×n×(hop count), when (distance between nodes)×n≦(reachabledistance of radio wave)<(distance between nodes)×(n+1) is true. In thismanner, the determining apparatus 110 calculates the estimated distancebased on a product of the distance between nodes of the node group 102,hop count, and a coefficient corresponding to the reachable distance ofthe wireless signals transmitted by the nodes of the node group 102. Asa result, the estimated distance can be calculated with high accuracy.

Further, when (reachable distance of radio wave)<(distance betweennodes) is true, transmitted wireless signals cannot reach other nodesand the configuration fails as a sensor network. In this case, thedetermining apparatus 110 may output alarm information to the user.

In FIG. 8, although description has been given assuming that the nodes811 to 816 are arranged at even intervals in a straight line, thedistance 802 between nodes may be calculated taking into consideration acase where the nodes 811 to 816 are not arranged at even intervals or ina straight line. For example, the determining apparatus 110 calculatesthe area of the partial area 801. Assuming the actual distance betweenthe monitoring apparatus 121 and the monitoring apparatus 126 is L, alength of the partial area 801 along a lateral direction is L. Further,a length of the partial area 801 along a longitudinal direction isassumed to be a length that is 3/2 of the average distance 802 (1/√ρ)between nodes.

In this case, the determining apparatus 110 can calculate the area ofthe partial area 801 between the monitoring apparatus 121 and themonitoring apparatus 126 by L·(1/√ρ)·(⅔). Therefore, the determiningapparatus 110 can calculate the number of nodes actually in the partialarea 801 by L·(1/√ρ)·(⅔)·ρ).

The determining apparatus 110 divides the actual distance L between themonitoring apparatus 121 and the monitoring apparatus 126 by thecalculated number of nodes in the partial area 801. In other words, thedetermining apparatus 110 calculates (1/√ρ)·(3/2). As a result,distances between nodes can be calculated taking into considerationdifferences in the distribution of the nodes.

Thus, the determining apparatus 110 according to the first embodimentcalculates an estimated distance between monitoring apparatuses based onhop counts of wireless signals transmitted and received (via the nodegroup 102) by the nearby monitoring apparatuses 121 to 128 of the nodegroup 102. The determining apparatus 110 compares the estimated distanceand the actual distance and thereby, can make a determination about avacant area 103 void of a node.

Further, the determining apparatus 110 uses the monitoring apparatuses121 to 128 provided encompassing the given area 101 and the node group102 scattered in the given area 101 and thereby, for example, can make adetermination about the vacant area 103 more easily than by using avisual survey, measurement instrument such as an X ray imaging device, asonic survey, etc.

For example, in the determining system 100 depicted in FIGS. 1 and 2,although description of a case in which eight monitoring apparatuses(the monitoring apparatuses 121 to 128) are used to make a determinationabout the vacant area 103, two or more monitoring apparatuses may beused. For example, by using two or more monitoring apparatuses, one ormore combinations of monitoring apparatuses for which the difference ofthe estimated distance and the actual distance is a threshold or greatercan be extracted and therefore, the presence/absence of a vacant area103 and a straight line that includes the position at which a vacantarea 103 exists can be determined. Further, for example, by using fouror more monitoring apparatuses, position coordinates where a vacant area103 exists can be calculated and therefore, the position of a vacantarea 103 can be determined.

FIG. 9 is a diagram depicting an example of the determining systemaccording to a second embodiment. In FIG. 9, portions identical to thosedepicted in FIGS. 1 and 2 are given the same reference numerals used inFIGS. 1 and 2, and description thereof is omitted. As depicted in FIG.9, a determining system 900 according to the second embodiment includesa determining apparatus 910 and monitoring apparatuses 921 to 923. Themonitoring apparatuses 921 to 923 respectively, for example, may be anyof the monitoring apparatuses 121 to 128 depicted in FIGS. 1 and 2. Themonitoring apparatuses 921 to 923 are provided so as to encompass thegiven area 101.

The determining apparatus 910 is an apparatus that can communicate withthe monitoring apparatuses 921 to 923. Further, the determiningapparatus 910 may be an apparatus that is provided separately from themonitoring apparatuses 921 to 923, or may be an apparatus that isprovided in any one of the monitoring apparatuses 921 to 923. In theexample depicted in FIG. 9, the determining apparatus 910 is provided inthe monitoring apparatus 921.

The given area 101 depicted in FIG. 9, similar to the given area 101depicted in FIG. 1, has the node group 102 scattered therein and thevacant area 103 in which no node is present. A target node 901 includedin the node group 102 is assumed to have transmitted a wireless signalin a vicinity thereof. For example, the target node 901 transmits awireless signal indicating sensing results obtained by a sensor of thetarget node 901. The wireless signal transmitted by the target node 901is multi-hop transferred by the node group 102 while the hop countindicated by hop count information is incremented, and the wirelesssignal is received by the monitoring apparatuses 921 to 923. Themonitoring apparatuses 921 to 923 transmit to the determining apparatus910, the hop count information of the received wireless signal.

The determining apparatus 910 is a determining apparatus that determinesthe position of the target node 901. More specifically, the determiningapparatus 910 calculates based on the hop count information receivedfrom the monitoring apparatuses 921 to 923, estimated distances betweenthe target node 901 and the monitoring apparatuses 921 to 923. Thecalculation of the estimated distances based on the hop countinformation, for example, can be performed by the method depicted inFIG. 8.

Based on the calculated estimated distances, the determining apparatus910 calculates estimation curves 931 to 933 that originate at themonitoring apparatuses 921 to 923, respectively. For example, theestimation curve 931 is centered about the monitoring apparatus 921 andis an arc whose radius is the estimated distance between the target node901 and the monitoring apparatus 921.

Further, the determining apparatus 910 obtains vacant area informationthat indicates the range of the vacant area 103. The vacant areainformation, for example, is input to the determining apparatus 910 bythe user and is stored to the memory of the determining apparatus 910.For example, the user measures the position of the vacant area 103 inthe given area 101. Measurement of the position of the vacant area 103,for example, can be performed using a visual survey, a measuringinstrument (X ray imaging device, etc.), sonic survey, and the like.Further, the determination result by the determining apparatus 110 maybe used as the vacant area information.

Since the vacant area 103 is present between the estimation curve 932and the monitoring apparatus 922, the determining apparatus 910 correctsthe estimation curve 932 based on the vacant area information, whichindicates the range of the vacant area 103. Estimation curve correctionbased on the vacant area information will be described hereinafter (forexample, refer to FIG. 10. An estimation curve 932 a is the estimationcurve 932 after correction. The determining apparatus 910 calculatesintersections of the estimation curves 931, 932 a, 933 and thereby,determines the position of the target node 901. As a result, theposition of the target node 901, which is the transmission source of thewireless signal, can be determined more accurately.

FIG. 10 is a diagram (part 1) depicting an example of estimation curvecorrection by the determining system. In FIG. 10, portions identical tothose in FIG. 9 are given the same reference numerals used in FIG. 9 anddescription thereof is omitted. For example, the monitoring apparatus921 and the monitoring apparatus 922 are assumed to be arranged tosandwich the vacant area 103.

<Calculation of Effect Level Per Unit Length of Vacant Area>

The determining apparatus 910 calculates for the estimated distancebased on hop count, the effect level per unit length of the vacant area103. More specifically, the determining apparatus 910 causes a surveysignal (wireless signal) to be transmitted and received between themonitoring apparatus 921 and the monitoring apparatus 922, by multi-hopcommunication by the node group 102 and thereby, obtains the hop countof the wireless signal between the monitoring apparatus 921 and themonitoring apparatus 922. The determining apparatus 910 calculates anestimated distance between the monitoring apparatus 921 and themonitoring apparatus 922, based on the obtained hop count. Thecalculation of estimated distance based on hop count is identical to theestimated distance calculation depicted in FIG. 8.

The determining apparatus 910 obtains distance information thatindicates the actual distance between the monitoring apparatus 921 andthe monitoring apparatus 922. The distance information, for example, isstored in the memory of the determining apparatus 910, in advance. Thedetermining apparatus 910 may obtain the distance information by acalculation based on information indicating the position coordinates ofthe monitoring apparatuses 921, 922. The position coordinates of themonitoring apparatuses 921, 922, for example, may be stored in thememory of the determining apparatus 910, in advance or may be obtainedfrom the monitoring apparatuses 921, 922.

The determining apparatus 910 calculates the difference of the estimateddistance and actual distance between the monitoring apparatus 921 andthe monitoring apparatus 922.

The determining apparatus 910 calculates a straight line connecting themonitoring apparatus 921 and the monitoring apparatus 922. Morespecifically, the position coordinates of the monitoring apparatuses921, 922 are assumed to be (x1, y1) and (x2, y2), respectively. Thedetermining apparatus 910 can calculate a straight line connecting themonitoring apparatuses 921, 922 by substituting x1, y1, x2, y2 into(y2−y1)x+(x2−x1)y+x2y1−x1y2=0. In the example depicted in FIG. 10, astraight line 1010 is calculated.

The determining apparatus 910 calculates intersections of the calculatedstraight line 1010 and the border of the vacant area 103. Morespecifically, the determining apparatus 910 calculates the solution to asystem of equations including an equation representing the straight line1010 and an equation representing the range of the vacant area 103 andthereby, calculates intersections of the straight line 1010 and theborder of the vacant area 103. In the example depicted in FIG. 10,intersections 1021, 1022 are calculated.

The determining apparatus 910 calculates the distance between theintersections 1021, 1022. The determining apparatus 910 divides thedifference of the estimated distance and the actual distance between themonitoring apparatus 921 and the monitoring apparatus 922 by thedistance between the intersections 1021, 1022. As a result, in theestimated distance based on hop count, the effect level per unit lengthof the vacant area 103 can be calculated.

<Estimation Curve Calculation>

FIG. 11 is a diagram (part 2) depicting an example of estimation curvecorrection by the determining system. The determining apparatus 910calculates an arc whose center is at the position coordinates of themonitoring apparatus 922 and whose radius is the estimated distancebetween the target node 901 and the monitoring apparatus 922, based onthe hop count from the target node 901 (refer to FIG. 9). As a result,an estimation curve 1110 based on the monitoring apparatus 922 can becalculated.

The determining apparatus 910 determines whether at least one portion ofa vacant area 103 is present between the position coordinates of themonitoring apparatus 922 and the estimation curve 1110. If no vacantarea 103 is present between the position coordinates of the monitoringapparatus 922 and the estimation curve 1110, the determining apparatus910 does not correct the estimation curve 1110.

If at least one portion of a vacant area 103 is present between theposition coordinates of the monitoring apparatus 922 and the estimationcurve 1110, the determining apparatus 910 selects a point 1111 on theestimation curve 1110 and calculates a straight line 1112 connecting themonitoring apparatus 922 and the point 1111.

For example, the position coordinates of the monitoring apparatus 922are assumed to be (x0, y0), and a point (x1, y1) on the perimeter of acircle whose radius is r satisfies (x1−x0)²+(y1−y0)²=r². Therefore, astraight line passing through the point 1111 and the positioncoordinates (x0, y0) of the monitoring apparatus 922 is(x−x1)/(x0−x1)=(y−y1)/(y0−y1).

The determining apparatus 910 calculates the distance betweenintersections 1121, 1122 of the straight line 1112 and the vacant area103, if the calculated straight line 1112 has a portion overlapping thevacant area 103. For example, the position coordinates of theintersections 1121, 1122 are assumed to be (x1, y1) and (x2, y2), andthe distance between the intersections is √((x2−x1)²+(y2−y1)²).Therefore, the length of the portion of the straight line 1112overlapping the vacant area 103 can be calculated.

The determining apparatus 910 multiplies the obtained effect level perunit length of the vacant area 103 by the calculated distance betweenthe intersections 1121, 1122. As a result, the effect level of thevacant area 103 at the point 1111 can be calculated.

The determining apparatus 910 causes the point 1111 to move by thedistance of the calculated product, toward the position coordinates ofthe monitoring apparatus 922. The point 1111 a is the point 1111 aftermovement toward the position coordinates of the monitoring apparatus922, by the distance of the calculated product. More specifically, thedetermining apparatus 910 calculates the point 1111 a by calculating thepoint (x, y), which is (x−x1)/(x0−x1)=(y−y1)/(y0−y1) and(x1−x)²⁺(y1−y)²=(effect level of vacant area 103 at point 1111)². As aresult, the point 1111 on the estimation curve 1110 can be correctedbased on the effect level of the vacant area 103.

FIG. 12 is a diagram (part 3) depicting an example of estimation curvecorrection by the determining system. As depicted in FIG. 12, byperforming the correction performed for the point 1111 on the estimationcurve 1110 with respect to other points on the estimation curve 1110,the determining apparatus 910 can obtain an estimation curve 1110 a,which is the estimation curve 1110 after correction based on the effectlevel of the vacant area 103.

The determining apparatus 910 and the monitoring apparatuses 921 to 923,for example, can be realized by the information processing apparatus 300depicted in FIG. 3. The determining apparatus 910 and the monitoringapparatuses 921 to 923 may be realized by separate informationprocessing apparatuses 300 or may be realized by a single informationprocessing apparatus 300. Further, the determining apparatus 110according to the first embodiment and the determining apparatus 910according to the second embodiment can be realized by a singleinformation processing apparatus 300.

FIG. 13 is a diagram depicting an example of a configuration of thedetermining apparatus according to the second embodiment. As depicted inFIG. 13, the determining apparatus 910 according to the secondembodiment includes an obtaining unit 1301, a calculating unit 1302, acorrecting unit 1303, and a determining unit 1304.

The obtaining unit 1301 regards each of the monitoring apparatuses 921to 923 as a target monitoring apparatus and obtains hop countinformation indicating the hop count for a wireless signal transmittedfrom a target node 901 (target wireless communications apparatus) and tobe received by the target monitoring apparatus by multi-hopcommunication by the node group. The obtaining unit 1301 notifies thecalculating unit 1302 of the hop count indicated by the obtained hopcount information.

The calculating unit 1302 regards each of the monitoring apparatuses 921to 923 as a target monitoring apparatus, and calculates an estimateddistance between the target monitoring apparatus and the target node901, based on the hop count notified from the obtaining unit 1301. Thecalculating unit 1302 regards each of the monitoring apparatuses 921 to923 as a target monitoring apparatus and calculates based on thecalculated estimated distance, an estimation line (estimation curve)that indicates candidates of the position of the target node 901. Thecalculating unit 1302 notifies the correcting unit 1303 of thecalculated estimation curve.

The correcting unit 1303 obtains vacant area information indicating therange of a vacant area 103 in which no node of the node group 102 of thegiven area 101 is present. The correcting unit 1303 regards each of themonitoring apparatuses 921 to 923 as a target monitoring apparatus andcorrects based on the obtained vacant area information, the estimationcurve notified by the calculating unit 1302. The correcting unit 1303notifies the determining unit 1304 of the corrected estimation curve.

The determining unit 1304 determines the position of the target node 901based on an intersection of the estimation curves notified by thecorrecting unit 1303. The determining unit 1304 outputs a determinationresult.

The obtaining unit 1301, for example, can be realized by the CPU 301 andthe communications unit 303 depicted in FIG. 3. The calculating unit1302, the correcting unit 1303, and the determining unit 1304, forexample, can be realized by the CPU 301 depicted in FIG. 3. Further, thedetermination result output from the determining unit 1304, for example,is output to an external destination by the communications unit 303and/or the input/output interface 305.

FIG. 14 is a flowchart depicting an example of determination operationof the determining apparatus according to the second embodiment. Thedetermining apparatus 910 according to the second embodiment, forexample, executes the following operations. The determining apparatus910 determines whether estimation curves based on each of the monitoringapparatuses (the monitoring apparatuses 921 to 923) have been calculated(step S1401). If an estimation curve has not be calculated for any oneof the monitoring apparatuses (step S1401: NO), the determiningapparatus 910 obtains vacant area information (step S1402). Theobtaining of the vacant area information may be performed before stepS1401.

The determining apparatus 910 obtains the hop count of the wirelesssignal, i.e., the hop count from the target node 901 to the targetmonitoring apparatus for which no estimation curve has been calculated(step S1403). The determining apparatus 910 calculates an estimateddistance between the target monitoring apparatus and the target node901, based on the hop count obtained at step S1403 (step S1404).

The determining apparatus 910, as an estimation curve based on thetarget monitoring apparatus, calculates a circle whose center is thetarget monitoring apparatus and whose radius is the estimated distancecalculated at step S1404 (step S1405). The determining apparatus 910determines based on the vacant area information obtained at step S1402,whether a vacant area is present between the target monitoring apparatusand the estimation curve calculated at step S1405 (step S1406).

At step S1406, if no vacant area is present (step S1406: NO), thedetermining apparatus 910 returns to step S1401. If a vacant area ispresent (step S1406: YES), the determining apparatus 910 corrects basedon the vacant area information obtained at step S1402, the estimationcurve calculated at step S1405 (step S1407), and returns to step S1401.The estimation curve correction will be described hereinafter (forexample, refer to FIG. 15).

At step S1401, if estimation curves based on each of the monitoringapparatuses have been calculated (step S1401: YES), the determiningapparatus 910 calculates intersections of the calculated estimationcurves (step S1408). The determining apparatus 910 calculates the centerof gravity of the intersections calculated at step S1408 and thereby,determines the position of the target node (step S1409), and ends aseries of operations.

FIG. 15 is a flowchart depicting an example of correction operation ofthe determining apparatus according to the second embodiment. Thedetermining apparatus 910, for example, executes the followingoperations as the estimation curve correction operation at step S1407depicted in FIG. 14.

The determining apparatus 910 obtains the effect level per unit lengthof the vacant area indicated by the vacant area information (stepS1501). The determining apparatus 910 determines whether points on theestimation curve based on the target monitoring apparatus have beensubject to processing at step S1503 described hereinafter (step S1502).If the points on the estimation curve have not been processed (stepS1502: NO), the determining apparatus 910 regards an unprocessed pointamong the points on the estimation curve as a target point, andcalculates a straight line connecting the target point and the targetmonitoring apparatus (step S1503).

The determining apparatus 910 determines based on the vacant areainformation, whether a portion of the straight line calculated at stepS1503 overlaps the vacant area (step S1504). If no overlapping portionis present (step S1504: NO), the determining apparatus 910 returns tostep S1502. If an overlapping portion is present (step S1504: YES), thedetermining apparatus 910 calculates the length of the portion of thestraight line calculated at step S1503 and overlapping the vacant area(step S1505).

The determining apparatus 910 multiples the effect level per unit lengthobtained at step S1501 by the length of the overlapping portioncalculated at step S1505 (step S1506). The determining apparatus 910causes the target point on the estimation curve based on the targetmonitoring apparatus to move toward the target monitoring apparatus bythe distance of the product calculated at step S1506 (step S1507), andreturns to step S1502.

At step S1502, if the points on the estimation curve have been processed(step S1502: YES), the determining apparatus 910 ends a series of thecorrection operations. As a result, the estimation curve can becorrected based on the vacant area information.

Thus, based on the range of the vacant area 103, in which no node ispresent, the determining apparatus 910 according to the secondembodiment corrects the node-position estimation curves 931 to 933 thatare based on the hop count from the target node 901 to the monitoringapparatuses 921 to 923. As a result, even if a vacant area 103 ispresent between the target node 901 and any one of the monitoringapparatuses 921 to 923, the position of the target node 901 can bedetermined with good accuracy.

Further, by combining the first embodiment and the second embodiment, adetermining apparatus can be realized that executes determinationconcerning the vacant area 103 and determination of the position of thetarget node 901 based on the determination result of the vacant area 103and the hop count.

The determining method described in the present embodiment may beimplemented by executing a prepared program on a computer such as apersonal computer and a workstation. The program is stored on anon-transitory, computer-readable recording medium such as a hard disk,a flexible disk, a CD-ROM, an MO, and a DVD, read out from thecomputer-readable medium, and executed by the computer. The program maybe distributed through a network such as the Internet.

In each of the embodiments described, although a configuration has beendescribed that determines position based on 2-dimensional positioncoordinates, the configuration may be one that determines position basedin 3-dimensional position coordinates. For example, a straight linepassing through two 3-dimensional position coordinates (x1, y1, z1),(x2, y2, z2) can be calculated by(x−x1)/(x2−x1)=(y−y1)/(y2−y1)=(z−z1)/(z2−z1).

Further, the center of gravity of three or more 3-dimensional positioncoordinates (x1, y1, z1), (x2, y2, z2), . . . , (xm, ym, zm) can becalculated by ((x1+x2+ . . . +xm)/m, (y1+y2+ . . . +ym)/m, (z1+z2+ . . .+zm)/m).

The distance between two 3-dimensional position coordinates (x1, y1,z1), (x2, y2, z2) can be calculated by √((x2−x1)²+(y2−y1)²+(z2−z1)²).

A sphere whose center is at the 3-dimensional position coordinates (x1,y1, z1) and whose radius is r, can be calculated by(x−x1)²+(y−y1)²+(z−z1)²=r².

Further, a point (x1, y1, z1) on the surface of the sphere whose centeris at the 3-dimensional position coordinates (x0, y0, z0) and whoseradius is r, can be calculated by (x1−x0)²+(y1−y0)²+(z1−z0)²=r². Astraight line passing through the point (x1, y1, z1) on the surface ofthe sphere and the center of the sphere (x0, y0, z0) can be calculatedby (x−x1)/(x0−x1)=(y−y1)/(y0−y1)=(z−z1)/(z0−z1).

A point that results by moving the 3-dimensional position coordinates(x1, y1, z1) a given distance can be calculated by calculating a point(x, y, z) that is (x−x1)/(x0−x1)=(y−y1)/(y0−y1)=(z−z1)/(z0−z1) and(x1−x)²+(y1−y)²+(z1−z)²=(given distance)².

Further, the distance between nodes in the given area 101 can becalculated based on the density [node/area] of the node group 102 in thegiven area 101. For example, the distance between nodes in the givenarea 101 can be calculated by 1/ρ^(1/3), where ρ is the density of thenode group 102 in the given area 101.

According to one aspect of the present invention, an effect is achievedin that node-vacant areas can be determined.

All examples and conditional language provided herein are intended forpedagogical purposes of aiding the reader in understanding the inventionand the concepts contributed by the inventor to further the art, and arenot to be construed as limitations to such specifically recited examplesand conditions, nor does the organization of such examples in thespecification relate to a showing of the superiority and inferiority ofthe invention. Although one or more embodiments of the present inventionhave been described in detail, it should be understood that the variouschanges, substitutions, and alterations could be made hereto withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A determining method executed by a processor, thedetermining method comprising: obtaining distance information thatindicates a distance between monitoring apparatuses disposed toencompass a given area in which wireless communications apparatuses arescattered; causing a wireless signal to be transmitted and receivedbetween the monitoring apparatuses by multi-hop communication among thewireless communications apparatuses; calculating an estimated distancebetween the monitoring apparatuses, based on a hop count of the wirelesssignal multi-hop communicated among the monitoring apparatuses; andmaking a determination concerning a vacant area in which none of thewireless communications apparatuses is present, based on a result ofcomparison of the distance indicated by the obtained distanceinformation and the calculated estimated distance.
 2. The determiningmethod according to claim 1, wherein the monitoring apparatuses includeat least four monitoring apparatuses encompassing the given area, theobtaining includes obtaining the distance information for respectivecombinations of the monitoring apparatuses, the calculating includescalculating the estimated distance for the respective combinations ofthe monitoring apparatuses, and the making of the determination includesextracting from among the respective combinations of the monitoringapparatuses, a combination for which a difference of the distanceindicated by the distance information and the estimated distance is atleast a threshold, and determining a position of the vacant area, basedon an extraction result.
 3. The determining method according to claim 2,wherein the making of the determination includes when the combinationfor which the difference is at least the threshold is extracted inplural, calculating for each extracted combination, a straight lineconnecting the monitoring apparatuses of the combination, anddetermining the position of the vacant area, based on an intersection ofthe calculated straight lines.
 4. The determining method according toclaim 3, wherein the making of the determination includes when thecombination for which the difference is at least the threshold isextracted in a plurality of at least three combinations, calculatingintersections of the straight lines, and determining a range of thevacant area, based on a center of gravity of the calculatedintersections and the intersections.
 5. The determining method accordingto claim 4, wherein the making of the determination includes determiningthat a range encompassed by a circle that has a center at the center ofgravity and includes the intersections is the vacant area.
 6. Thedetermining method according to claim 5, wherein the making of thedetermination includes calculating a greatest value among distancesbetween the center of gravity and each of the intersections, anddetermining that the range encompassed by the circle that has a centerat the center of gravity and a radius of the calculated greatest valueis the vacant area.
 7. The determining method according to claim 1,wherein the calculating includes calculating the estimated distancebased on the hop count and, a distance between the wirelesscommunications apparatuses and calculated from a density of the wirelesscommunications apparatuses in the given area.
 8. The determining methodaccording to claim 7, wherein the calculating includes calculating theestimated distance based on a product of the distance between thewireless communications apparatuses, the hop count, and a coefficientcorresponding to a reachable distance of the wireless signal transmittedby the wireless communications apparatuses.
 9. The determining methodaccording to claim 1, wherein the monitoring apparatuses transmit thewireless signal at a power equal to the power at which the wirelesscommunications apparatuses transmit the wireless signal.
 10. Thedetermining method according to claim 1, wherein each monitoringapparatus among the monitoring apparatuses, when receiving from multiplepaths of the wireless communications apparatuses, the wireless signalfor which a transmission source is identical, obtains the hop count thatis smallest among the hop counts of the received wireless signal.
 11. Anon-transitory, computer-readable recording medium that stores therein,a determining program causing a computer to execute a processcomprising: obtaining distance information that indicates a distancebetween wireless communications apparatuses disposed to encompass agiven area in which wireless communications apparatuses are scattered;causing a wireless signal to be transmitted and received between themonitoring apparatuses by multi-hop communication among the wirelesscommunications apparatuses; calculating an estimated distance betweenthe monitoring apparatuses, based on a hop count of the wireless signalmulti-hop communicated among the monitoring apparatuses; and making adetermination concerning a vacant area in which none of the wirelesscommunications apparatuses is present, based on a result of comparisonof the distance indicated by the obtained distance information and thecalculated estimated distance.
 12. A determining apparatus comprising: astorage apparatus storing therein information received from wirelesscommunications apparatuses disposed to encompass a given area in whichwireless communications apparatuses are scattered; and a processingapparatus that processes the information stored in the storageapparatus, wherein the processing apparatus: obtains distanceinformation indicating a distance between the monitoring apparatuses,causes a wireless signal to be transmitted and received between themonitoring apparatuses by multi-hop communication among the wirelesscommunications apparatuses, calculates an estimated distance between themonitoring apparatuses, based on a hop count of the wireless signalmulti-hop communicated among the monitoring apparatuses, and makes adetermination concerning a vacant area in which none of the wirelesscommunications apparatuses is present, based on a result of comparisonof the distance indicated by the obtained distance information and thecalculated estimated distance.
 13. A determining system comprising:wireless communications apparatuses disposed to encompass a given areain which wireless communications apparatuses are scattered; and adetermining apparatus that includes: a storage apparatus storing thereininformation received from the monitoring apparatuses; a processingapparatus that processes the information stored in the storageapparatus, wherein processing apparatus: obtains distance informationindicating a distance between the monitoring apparatuses, causes awireless signal to be transmitted and received between the monitoringapparatuses by multi-hop communication among the wireless communicationsapparatuses, calculates an estimated distance between the monitoringapparatuses, based on a hop count of the wireless signal multi-hopcommunicated among the monitoring apparatuses, and makes a determinationconcerning a vacant area in which none of the wireless communicationsapparatuses is present, based on a result of comparison of the distanceindicated by the obtained distance information and the calculatedestimated distance.
 14. A determining method executed by a processor,the determining method comprising: obtaining distance information thatindicates a distance between first monitoring apparatuses disposed toencompass a given area in which wireless communications apparatuses arescattered; causing a wireless signal to be transmitted and receivedbetween the first monitoring apparatuses by multi-hop communicationamong the wireless communications apparatuses; calculating an estimateddistance between the first monitoring apparatuses, based on a hop countof the wireless signal multi-hop communicated among the first monitoringapparatuses; and making a determination concerning a vacant area inwhich none of the wireless communications apparatuses is present, basedon a result of comparison of the distance indicated by the obtaineddistance information and the calculated estimated distance; obtainingfor each monitoring apparatus among second monitoring apparatusesdisposed to encompass the given area, hop count information thatindicates a hop count for a wireless signal that is transmitted from atarget wireless communications apparatus included in the wirelesscommunications apparatuses, to be received by the monitoring apparatusby the multi-hop communication among the wireless communicationsapparatuses; calculating an estimation line that indicates a candidateof a position of the target wireless communications apparatus, theestimation line being calculated for each monitoring apparatus among thesecond monitoring apparatuses, and calculated from an estimated distancebetween the monitoring apparatus and the target wireless communicationsapparatus, the estimated distance being based on the hop count indicatedby the obtained hop count information; correcting for each monitoringapparatus among the second monitoring apparatuses, the calculatedestimation line, based on a determination result concerning the vacantarea; and determining a position of the target wireless communicationsapparatus, based on intersection of the corrected estimation line.